package org.springframework.http.server.reactive;

import java.util.LinkedHashMap;
import java.util.Map;

import reactor.core.publisher.Mono;

import org.springframework.http.HttpStatus;
import org.springframework.util.Assert;

/**
 * {@code HttpHandler} delegating requests to one of several {@code HttpHandler}'s
 * based on simple, prefix-based mappings.
 *
 * <p>This is intended as a coarse-grained mechanism for delegating requests to
 * one of several applications -- each represented by an {@code HttpHandler}, with
 * the application "context path" (the prefix-based mapping) exposed via
 * {@link ServerHttpRequest#getPath()}.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class ContextPathCompositeHandler implements HttpHandler {

    private final Map<String, HttpHandler> handlerMap;


    public ContextPathCompositeHandler(Map<String, ? extends HttpHandler> handlerMap) {
        Assert.notEmpty(handlerMap, "Handler map must not be empty");
        this.handlerMap = initHandlers(handlerMap);
    }

    private static Map<String, HttpHandler> initHandlers(Map<String, ? extends HttpHandler> map) {
        map.keySet().forEach(ContextPathCompositeHandler::assertValidContextPath);
        return new LinkedHashMap<>(map);
    }

    private static void assertValidContextPath(String contextPath) {
        Assert.hasText(contextPath, "Context path must not be empty");
        if (contextPath.equals("/")) {
            return;
        }
        Assert.isTrue(contextPath.startsWith("/"), "Context path must begin with '/'");
        Assert.isTrue(!contextPath.endsWith("/"), "Context path must not end with '/'");
    }


    @Override
    public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
        // Remove underlying context path first (e.g. Servlet container)
        String path = request.getPath().pathWithinApplication().value();
        return this.handlerMap.entrySet().stream()
                .filter(entry -> path.startsWith(entry.getKey()))
                .findFirst()
                .map(entry -> {
                    String contextPath = request.getPath().contextPath().value() + entry.getKey();
                    ServerHttpRequest newRequest = request.mutate().contextPath(contextPath).build();
                    return entry.getValue().handle(newRequest, response);
                })
                .orElseGet(() -> {
                    response.setStatusCode(HttpStatus.NOT_FOUND);
                    response.setComplete();
                    return Mono.empty();
                });
    }

}
